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An important aspect to setting up your lights

Discussion in 'General Plant Topics' started by ntino, Dec 17, 2008.

  1. ntino

    ntino Guru Class Expert

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    I have been waiting to make this post for a while now.

    Waiting because I have long suspected that uniform light intensity is the real deal with lighting. The new apogee meter I got confirmed what I thought to be true.

    Here is an example - you can have 100w over a tank and 400w of lights over a tank and have the same light levels in the middle of your tank. To achieve that, you would of course need to place the lights at different hights above the water.

    However, with the 100w light that is close to the water you wont have the same light intensity throughout the tank - you will have alot of light at the top, and very little light at the bottom of the tank.
    On the other hand, with a high output light mounted high above the tank, you will have much more uniform intensity.

    Here is a real example - I have a newly set up cube tank that is 24" deep. I chose to go with a ceiling suspended MH light for a cleaner look. I could have gone with a 150w of light, which would give me good light levels with the light suspended 6"-8" from the water, however, this setup would create hot spots at the top of the tank, and much less light at the bottom - this would most likely lead to algae on the top leafs, especially if I wanted to place anubias or any low light plants at the top.

    Instead, I went with a 250w light, suspended about 18" above the water, and this gives me an intensity of 100-110PAR at the top and 70-75" PAR at the substrate - this is alot better than the 140 on top and 40 at the bottom that I would have gotten with a 150w light.
    These measurements were taken with an apogee PAR meter.

    Some might say that this wastes alot of light - while this might be true, this is the only way to create a uniform intensity throughout the tank - think of it this way - the sun shines the same whether you are up on a mountain or bellow sea level because its a very big light source far away.

    So when you consider buying new lights for your setup - consider buying a high output light but mount it higher up - you can even make a box around the light to prevent accessive light spill.
     
  2. Tom Barr

    Tom Barr Founder
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    This is true, now ask yourself "why".

    It has to do with light spread.
    A simple theoretical model of a light bulb's output and the ability to distribute the light evenly across the tank is something I've mentioned for many years.

    A single PC light with the same watt/PAR, will not have the same/as good, as growth as 2-3 T8's with the same wattage and par overall, the difference is the spread and various angles the light energy hits the plant leaves.

    Basically what you have stated above. The evenness and spread.
    You get a hot spot with the PCand then not much elsewhere.
    Then you get algae there, either real good growth, or not much eslewhere etc.

    MH's:
    The diffraction and diffusion of the light increases in the MH example also, you get a real hot spot, and issues growing other plants well throughout the tank. It is likely even more pronounced with MH's.

    You often see lux spread areas for MH's, but those can and do change a lot as you use less/increase the light fixture distance etc. 6-8" is too close unless............you plan on moving the light as the day goes on, or have the light ona track to move it back and forth.

    My light stand allows me to move the lights any 3D direction, I have somethimes moves it down 4-6" above the water, then moved it back every couples of hours to get good spread. This gave me the fastest nicest growth.

    I had planned on putting a track rail moving system, but to do this, I think I'd have to spend a lot more and put it into the ceiling to look nice. I am not going to do that here where I now live. I will do this later however.

    But I also can easily raise the light to 15" or higher. I also have a bank of PC's in the MH fixture which I can switch off and on. These are placed wider apart from eachother than in any other brand name hood with the Coralife pro fixture(about 15" + wide pancake fixture- takes up more space, but is only 2.75" tall).

    This gives more even light and better spread, color etc and gets around the trade offs on one type vs another type of light.

    This way you can avoid using more light, higher fixturea and the evil light spray. I like the spray since I do not have to heat the house much or turn the house lights on.

    Your measurements show a good plan for those wanting less light or want to raise up the light and have enough light to still do well with plants, or when they leave for vacaton and want to slow the growth rates down.



    Regards,
    Tom Barr
     
  3. ntino

    ntino Guru Class Expert

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    Tom, thanks for the input but I wasnt actually talking about horizontal spread - this is usually well controlled for MH with a good reflector like the luminarc III which is big at 21".
    What I was talking about is vertical spread, which even a good reflector cannot help, nor will more spread out bulbs over a large area help - as long as you have them close to the water the top will recieve alot more light than the substrate. using more wattage and placing it farther away will help with that, because the distance from bulb does not change drastically with depth.
     
  4. ccLansman

    ccLansman Guru Class Expert

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    Having recently complete a course in electromagnetics I think I can also shed some "light" :) on this subject. Air and water have what is called an index of refraction. I won’t go into what that means but needless to say when light passes from one index of refraction into another if the two indexes are of different values the light gets "bent" and does not travel nicely between the two mediums. However this issue is easily solved by directing the light normal (90degrees) to the surface. When the light strikes the surface normal it has a much better chance of penetrating straight through. Thus when we place the HQI much further from the tank we see a much better penetration vs the PC light that is much closer and directing a lot more light not normal to the surface. If you ever want to experiment with this try taking a CF fixture and do a water change. Notice when the water is low the places furthest away from the light seem to be getting a lot of light. Well, refill the tank and simply look at the same spots.... Much less light....Ahhh... you have found the many wonders of the index of refraction. In equation form it is Tan(theta1)/Tan(theta2)=index1/index2. The index can also be seen when you try and pear down into the water from above the tank, it’s not easy to see inside. However glass and water have a better index ratio and you are looking normal you are easily able to see into the water.
    Hope this helps!
     
  5. Tom Barr

    Tom Barr Founder
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    Wow, a 21" reflector for the MH?
    That's plenty to address horizontal spread, huge.
    Ack, that would be a huge hood. I like small discrete hoods:)

    Yes, the same notion also applies to the vertical spread also if not more so since reflectors cannot address it. Then the differences are exponential as you move close to the light vertically(and horizontal as well).

    You also are looking at "lower light = better" also.

    The index of refraction plays a large role here as mentioned by ccLansman. Better angle the farther the distance for that area, you still lose light, but make it more even and not so hot in one spot. You should also reduce glass algae(both from intensity and from the angle).

    How might you think about this issue with PUR vs PAR?
    Think it makes a difference?

    Is losing some in one spot, better for the overall total growth throughout the tank using a point source light like HQI's? How about T5's? How would you predict those?


    Regards,
    Tom Barr
     
  6. Henry Hatch

    Henry Hatch Guru Class Expert

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    I noiced many of the same things using my Apogee par meter. I have a 50 gallon tank which is 18" wide. I had a single 3 bulb fixture with NO flourscent t8 bulbs sitting on top. When I took par readings at the back and front of the tank the par readings went down as I raised the sensor up from the substrate toward the surface presumably due to the acute angle of the light. The light started to drop about half way up.

    Many HO fixtures are narrow, particularly t5. If you have a tank more than 12" wide I think this is something that people should be aware of. I added another bulb in a single bulb fixture and that solved the problem.

    I wish vendors would pay more attention to the quality of reflectors as well as the shape.
     
  7. Tom Barr

    Tom Barr Founder
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    And the spacing.

    Many assume the more they can pack inot a smaller space, the better.
    Might be the case with marketing, but not practical applied issues or for planted tanks certainly either, and questionable in respect to reefs als, again, better angles and even spread might be preferred to a single intense hot spot.

    Regards,
    Tom Barr
     
  8. bgangler

    bgangler Junior Poster

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    Hi guys,
    sorry to interupting the discussion, but as Im reading the posts get to the conclusion that mixture of MH and T5 is not good, expecially in a tall tanks 50-60 cm? To not get hot spots and even distribution of the light, I need to put the MH higher lets say 30 -40cm above the water level, which will be to far for the T5?
    IS that correct? The thing is that I intend to make a fixture of lights - combination of T5 and MH and would like to try to simulate a sunrise and sunset, by doing diferent combination of light beeing swithed on and off.
    But know it seems pointless to me. ...
     
  9. If we consider light refraction, does it make sense to separate two T5 bulbs toward the front and back glasses? This would make the light hit front and back areas closer to a right angle, as well as give the chance for the light that goes to the middle area, with more angle, to hit the bottom? If the two bulbs were in the middle, angled light going to front and back areas would certainly hit the glass.
     
  10. VaughnH

    VaughnH Lifetime Charter Member
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    An interesting thing to do is, with your aquarium lights on, put your face down next to the front glass, and look through the tank up at the light. You can't see it, except near the bottom of the tank, if there. That means the light is striking the front glass and almost all of it is reflected back into the tank. At least that is how I interpret it. The practical meaning of this is that you get more light at the substrate with water in the tank, than without water in the tank, which is good. And, this means that the drop off in light intensity as you move down into the tank is less than would be predicted by an inverse square or linear relationship with distance. It also means that plants get light from more directions than just up towards the lights.
     
  11. bibbels

    bibbels Prolific Poster

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    This is interesting. I'll have to compare PAR readings on a 24gal cube that's in dry start phase now and see if values increase once I fill it.
     
  12. ntino

    ntino Guru Class Expert

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    PAR readings are not going to increase ones you fill the tank, especially if you use a sensor that is not a globe. if you did use a ball sensor, they would increase, but only if water is extremely clear, and prefferably the tank is a smaller cube.

    BTW, I was only reffering to vertical spread in my initial post, since I think its far more important than horizontal spread - if lights are placed wrong, it creates hot spots - which WILL cause algae, especially if plants are the slower growing kind.

    Right now, I moved my light down just a little bit, so that I get around 100 PAR at the bottom, and around 130 at the top - the tank was dry started, however for some reason, my HC wouldnt grow too well, and would yellow up alot in certain spots - slow grow overall, so I filled it with water - unfortuatenlly while I was doing it, I was on the phone with a buddy of mine, and forgot to dechlor the water, so the tank is cyclying again - ammonia is over 1ppm :(.
    because of low CO2 the PH is around 5.7, so I went ahead and added otos to combat abit of algae if it occurs, its been a week since I filled it with water, so far, no algae or green water, despite the ammonia.

    BTW, I would really recommend using as many pleat filters as you can - they really clear up the water - I did not have ANY cloudiness 1 hour after filling up in a tank with Aqua Soil even though water was very cloudy on fill up.

    Here are a few pics of the tank, Hc needs to grow in ect, plants havent really established themselves yet.

    [​IMG]
    [​IMG]
     
  13. Tom Barr

    Tom Barr Founder
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    Your tank is just starting to balance BTW. you need a bit more growth/grow in and things will get much better.

    I've been testing some things and making some notes about plant biomass relative to growth and plant domination of the aquarium.

    Once they get up to a certain % rooting and biomass, the tank takes off, otherwise is generally just sits.

    This issue was drawn out much longer and I was able to see it much better because fish kept uprooting plants in my 180 and in a 38. I was adding all the CO2 the same, the nutrients, water changes etc. Even if I did water changes at 60 every other day and Excel, nothing helped. Not until I added more biomass and allowed it to root well.

    Just a FYI, a good news flash rather than the other:p

    Regards,
    Tom Barr
     
  14. SuperColey1

    SuperColey1 Guru Class Expert

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    There are several points in this thread that vindicate wht I have said over the past year or so on other forums before being bashed for 'going against the grain'!!

    I have criticised PC lights for a long time since I used them for a period of 3 months before switching to T5HO.

    I always said that when I had PC lights the light was far too intense in a small area washing out the view of most of the top half of the tank. Also when these luminaires bang 4 T5 tubes in with less than an inch gap it has a similar effect.

    I always said in my posts that it would be much better to have several T8s spread out over the hood than to have equal wattage of PC close together!!!

    Would it not be advisable these days when we are retrofitting our lights these days to use high powered LEDs seeing as we can space them out even better then 2 or 3 tubes and they definately penetrate better???

    On the rooting front I have always found that the tank sems to take off after the roots have developed well. I have gone as far as to say that ferns, mosses and Anubias seem to do much better once they have properly attached.

    Good to know I wan't that far wrong whilst everyone else hammered me down :lol:

    AC
     
  15. Tom Barr

    Tom Barr Founder
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    I'd agree.

    Nope, I think it's a fair statement based on observation.
    I'm not sure about the LED's, but something along those lines or the T5's work nicer I think.

    They just need to make large spacing between the bulbs is all.
    I saw some nice hoods like this with 4 x T5's that where spaced nicely across the entire top of the tank in a nice hood, each bulb had it's own switch.

    Too bad that was in Portugal and not here.

    Really good light.

    Regards,
    Tom Barr
     
  16. ntino

    ntino Guru Class Expert

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    to be honest, t5 are really lacking compared to MH with newer reflectors or LED lights, but LED are not very good at coloring, atleast in reef tanks, but same applies to freshwater.
    The light t5s give off is alot more uniform, but that also creates a not so realistic look - there are little to no shadows also an MH pendant is a cleaner and easier to hang look most of the time, and you can hang them farther off the water for a much better vertical spread - no hotspots at the top.
     
  17. SuperColey1

    SuperColey1 Guru Class Expert

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    This depends on the colouration you like within your tank. Some people like the pink look and others like the blue of marine bulbs. Each to their own.

    I was thinking more about power consumption and lifespan of LEDs. Not the 5mm ones. I am talking 1W, 3W & 5W high powered.

    You could space 15x3W 5500K out over a tank and get 45W of light. If heatsinked properly then will be cooler than a fluorescent lamp or MH and will last a lot longer before needing replacing.

    AC
     
  18. ntino

    ntino Guru Class Expert

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    you can get about the same coloration with either mh or T5s even though t5s are abit easier to fine tune.

    LED are lacking in color - I have seen a few with my own eyes and alot of people on the reef side of things will tell you the same. right now LED systems also cost alot more than they should.
    I'm building a 500g reef system at the moment and was considering LEDs, but went with 400w moguls instead(note, not even HQI, though the ballast will be and HQI ballast to drive mogul lamps). If you are really interested in lighting, many reef folks have done alot of research - reef has abit more research behind it in general, since equipment is generally more expensive, for example, what is a very high light for a planted tank, is not nearly enough for hard corals in a reef tank, bigger lights = more heat, ect, so there are alot of issues when you go bigger and alot more money to spend too...
     
  19. SuperColey1

    SuperColey1 Guru Class Expert

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    I have to admit that I am on the verge of retrofitting an LED setup into my planted tank. When I mean on the verge I have no set deadline and am aiming for between Christmas and June.

    It isn't going to be a shop bought one and the items have cost approx £100.

    I am however doing it the 'ugly' way by butting 5 seperate series of 3 x 3W 5500Ks each series conected to a current controller and then a 12V 1000ma plug.

    This means 5 plugs but also means I can time the lights to stagger from left to right along the tank sunrise to sunset)

    So there are 5 rows of 3 LEDs, each with its own heatsink. There is a double fan at each end of the hood one sucking and one blowing to keep a flow of air through the lighting compartment and then a cut piece of glass between the lights and water surface.

    This will be 45W over a 33USG but I currently use a 30W T5HO and 18W T8 to good effect. I am expecting the output to be much more efficient but will be happy if it matches the current setup.

    So this LED setup costs £104 (approx). The T5HO and T8 (tube, ballast, reflector, timer) would cost a similar amount.

    Difference? The LEDs should last much much longer. The T5 is 4500K and T8 is 6500K so 5500K LEDs should be a similar output.

    Watch this space, maybe we will both be surprised ;)

    AC
     
  20. ntino

    ntino Guru Class Expert

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    Way to go!

    I'm no electrician, and wouldnt attempt to make something like this(seems like alot of effort to me), but here is what I know...

    Good LED setups are costly to make.
    There are several people on reefcentral.com that have made LED strips, fully dimmable, various colors of LED, ect. Both are electrical engineers and have experiece in this. Both took around 100h to make the fixture and over 1500$ in materials. Both claim that their fixtures are better than the current PFO ones, which are the leaders and cost 1800-4500 depending on size. However, both also stated that their fixtures are probably not as good as the old MH lights, as far as coloration goes.
    Watts per PAR and heat LED will obviously blow anything away due to LED physics.

    If you manage to make a smaller fixture for $180 it would be great - 15 power LEDs is way too much for such a small tank though, they would have an output that matches a 150w MH. One of the great things about LEDs is that they are fully dimmable with no adverse effects(which allows for endless possibilities as far as natural sun cycle imitation goes), make sure yours are.

    Make sure you post the build process on this so that others can learn!

    -Chris
     
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